Filament support for an electric lamp or similar device



April 18, 1961 W. L. BRUNDIGE ETAL FILAMENT SUPPORT FOR AN ELECTRIC LAMP OR SIMILAR DEVICE Filed Dec. 24, 1959 INVENTORS United States Patent 9 FILAMENT SUPPORT FOR AN ELECTRIC LAMP R SIMILAR DEVICE William L. Brundige, West Caldwell, and Raymond M.

Kane, Hanover, NJ., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Dec. 24, 1959, Ser. No. 861,861

7 Claims. (Cl. 313-279) .This invention relates to electrical devices and, more particularly, to an improved filament support assembly and member for an electric incandescent or heat lamp.

In US. Patent No. 2,813,993 dated November 19, 1957, there is disclosed and claimed a filament support structure for a tubular heat lamp or the like wherein a metal wafer or disc is inserted between adjacent turns and dis posed transversely to a coiled filament at spaced intervals along its length to centrally locate the filament within the lamp envelope. In order to prevent the disc from rotatively migrating or becoming laterally displaced from its mounted position on the filament it is locked to one of the adjacent filament turns by means of a collar and a plurality of adjoining tongues that are cut from the central part of the disc and partially wrapped around and thus made to interiorly grip the aforesaid filament turn. In accordance with the aforesaid patent, the locking collar and tongues are formed and caused to curl tightly around and thus grip the inner face of the engaged filament turn by means of a specially shaped tool that is inserted into the filament and pierces the disc after the latter has been positioned transversely on the filament.

While piercing and reshaping the center of the inserted disc in situ to couple it to the filament in the aforesaid fashion achieves the desired objective of securely locking the disc in place, the operation is rather difiicult to control and perform with consistently good results since it not only requires the formation of a properly contoured collar and tongues but the subsequent curling and wrapping thereof tightly around one of the filament turns. In addition, since the disc will only remain rigidly locked to the filament as long as the collar and tongues remain tightly seated against and thus grip the coil turn, extreme care must be exercised in handling the assembled filament and discs prior to and during the placement thereof into the envelope to avoid inadvertently striking or otherwise disturbing and thus loosening any of the protruding discs which would then be free to rotate about the axis of and migrate along the filament in the completed lamp.

It is accordingly the general object of this invention to provide an improved filament support construction for an electric lamp or similar device that will obviate the foregoing and other deficiencies of the prior art structures.

Another and more specific object of this invention is the provision ofa support assembly and member for a coiled filament or the like that will enable the support member to be consistently and positively locked in position on the filament by means of a simple inexpensive operation and maintained in such locked position during the completion and life of the device in which the filament is sealed.

The foregoing and other objects which will become apparent to those skilled in the art as the description proceeds are achieved in accordance with this invention by fabricating the supporting member from material that is greater in thickness than the spacing between the turns of the filament into which it is inserted. The resultant ice spreading of the adjacent turns of the filament causes them to compressively grip and thus firmly clamp the support in the desired transverse position on the filament. By properly correlating the thickness of the support member and the spacing between the filament turns the clamping force exerted by the displaced pair of adjacent turns on the support can be made large enough that the support will remain firmly locked in its inserted transverse position even though the filament is pulled taut when mounted and thus slightly distended to inhibit the sagging thereof in use.

A better understanding of the invention will be obtained by referring to the accompanying drawing wherem:

Fig. 1 is an elevational view of a tubular heat lamp incorporating the improved filament support assembly of this invention;

Fig. 2 is an enlarged cross-sectional view along the line II- -Il of Fig. 1, in the direction of the arrows;

Fig. 3 is an elevational side view partly in cross-section of a supported portion of the filament and the support member thereat taken along the line III-III of Fig. 2, in

the direction of the arrows;

Fig. 4 is a fragmentary cross-sectional view on a greatly enlarged scale through one of the supports and several of the adjacent filament turns taken along the line IVIV of Fig. 3, in the direction of the arrows;

Fig. 5 is a perspective view on an enlarged scale of a support and the associated portion of the filament, the central section of the filament being omitted to more clearly illustrate the structural details and disposition of the support member;

Fig. 6 is a fragmentary elevational view on a reduced scale of a preformed metal strip for facilitating the automatic insertion and assembly of the supports with the filment;

Fig. 7 is an elevational view on a reduced scale of another type of support member according to this invention; and

Fig. 8 is a fragmentary perspective view of another form of support and associated segment of the filament.

While the present invention may be advantageously employed in various types of electrical devices that have a coiled member which requires an auxiliary means of support, it is especially adapted for use with tubular heat lamps having a coiled filament of refractory wire and has accordingly been so illustrated and will be so described.

With reference to the drawing, in Fig. 1 there is illustrated a tubular heat lamp 10 comprising a quartz envelope 12 of relatively small diameter closed at each end by a press seal 17 and containing a heat generating element such as a linear filament 14 that is spaced from and extends axially within the envelope. The filament 14 comprises a plurality of equally spaced turns of refractory metal wire such as tungsten for example andis centrally positioned within the envelope 12 by .a plurality of transversely extending wafer-like support members such as discs 20 of tantalum or other suitable refractory material that are inserted between adjacent turns of and are anchored to the filament at preselected points along its length. Lead-in conductors 16 embedded in each of the press seals 17 and fastened to the ends of the filament 14 keep the latter taut and straight and connect it by means of the usual ribbon-and-outer-lead assemblies to sleeve-like base members 18 mounted on each of the press seals. A detailed description of this type lamp is given in US. Patent No. 2,864,025 dated December 9, I958.

As shown in Figs. 2 to 5, each of the discs 20 are split by an opening such as a slot 22 that extends radially inward from the periphery to approximately the center of the disc where it merges with an enlarged aperture 26 thereat. The discs 20 are preferably contoured to provide an outwardly tapered or flared entrance 24 into the slot 22 so as to facilitate the insertion of the discs into the filament 14. When assembled with the filament 14 the discs 20 are so disposed that the aperture 26 at the inward terminus of the slot 22 is centrally located within the interior of the filament and a portion of one of the adjacent filament turns passes through the slot, as illustrated in the aforesaid figures.

In accordance with the present invention the support discs 20 are so designed that when inserted between adjacent turns of the filament 14 they spread them apart and are, in turn, elastically gripped and firmly clamped thereby transversely of the filament axis. As shown more particularly in Fig. 4, this coaction between the aforesaid elements is achieved by correlating the finished dimensions of the filament 14 and the thickness of the refractory sheet material from which the discs are made. Specifically, the aforesaid parts are so dimensioned that the minimum thickness (T of the discs 20 is greater than the spacing between turns (S of the filament 14, that is, T S This requirement, expressed in terms of the design parameters of the filament, is defined by the following expression: P D +T where P is the pitch of the filament 14 and D the diameter of the wire from which it is wound. The aforesaid expressions are equivalent since S is equal to PD;. Obviously, where a family of filaments of different wattages and thus dimensions are involved the desired compressive clamping of the support members can be achieved by keeping one of the variables constant and properly correlating the others. With the particular type of heat lamp here illustrated, it has been found most convenient and practical to use the same disc and vary P and D as required to obtain the'proper number of turns, spacing between turns and wattage rating. Specific examples of this type approach are given below in the table designated Table I.

Table 1 Examples Variant I II III IV Lamp Wattage 500 1000 2500 1350 Turns Per Inch (t.p.i.) of the filament (finished) 98. 0 98. 0 93. 0 101.0 Diameter (Dr) of filament wir in inches 00910 00910 .00981 .00876 Minimum thickness (T of support memberlninches .00200 .00200 .00200 .00200 01110 01110 .01181 .01076 1 01020 01020 .01075 .00990 t.p.i.

It will be noted that in each of the examples given in Table I the pitch P is always less than D -j-T or, expressed diiferently, that S (i.e., PD is always less than T The difference between T and S preferably is made such that the discs 20 remain securely clamped between the filament turns even when the filament 14 is mounted under tension and is thus slightly distended.

While the discs 20 when compressively clamped in accordance with the foregoing will remain locked in their inserted positions under normal lamp-making conditions, it is preferable (as shown in Figs. 2 to 5) to provide auxiliary locking projections such as a plurality of toothlike burrs 28 at the margin of the aperture 26 to obviate any possibility whatsoever that the discs will inadvertently be displaced by an excessive amount laterally from their inserted positions during rough handling prior to or during the placement of the filament-and-disc assembly into the envelope 12. As shown more particularly in Fig. 4, the burrs 28 protrude transversely into the interior of the filament 14 from one side of the disc 20. However,

in contrast to the prior art practice, the aforesaid burrs are not wrapped tightly around and do not grip the adjacent filament turn but are merely disposed proximate thereto and are, in fact, normally spaced from the inner surface thereof. Thus, if any of the discs happen to he accidentally struck and forced from their mounted position by a force greater than the compressive clamping force exerted by the filament, then one or more'of the burrs will seat against the adjacent filament-turn and prevent the excessive lateral displacement of the discs prior to the insertion of the filament into the envelope. The aperture 26 and burrs'28 may be formed by a piercing tool after the discs have been inserted into the filament in a manner similar to that disclosed in the aforesaid U.S. Patent No. 2,813,993. It should be noted, however, that the discs 20 in accordance with the present invention are securely locked in place solely by the compressive clamping force produced by the displaced filament turns on opposite sides of each disc. The projections or burrs 28 merely serve as an auxiliary locking .means to avoid excessive lateral displacement of the manufacturing and cost standpoint over the aforementioned collar and tongue construction.

The support discs 20 may be automatically inserted into and assembled with the filament 14 by providing a preformed metal strip 30 such as that shown in Fig. 6. The strip 30 is slightly wider than the diameter of the discs 20 and is adapted to be sequentially inserted into the filament 14 and the discs formed in situ thereon by a suitable apparatus such as that disclosed in US. Patent No. 2,813,327 dated November 19, 1957.

In Fig. 7 there is illustrated another form of disc 200 having a plurality of slits '32 that extend radially from the inward terminus of the'opening 22a and define a plurality of triangular-shaped tabular segments 28a that can be very conveniently bent to provide the auxiliary locking projections referred to above. In this type disc the auxiliary locking elements are preformed, so to speak, and need only be displaced outwardly from the disc thereby eliminating the step of forming the projections in situ on the filament and further simplifying lamp manufacture.

In Fig. 8 there is shown still another type of disc 20b wherein the desired auxiliary locking means comprise a plurality of radially spaced projections such as tabs 34 that extend transversely from one or both sides of the disc and are thus disposed to engage the outer surface of the adjacent turn or turns thereat. Thus, the disc 20b is prevented from slipping laterally oif the filament 14 by auxiliary locking elements that are formed from portions of the disc that lie beyond the part thereof that is interposed between the adjacent turns of the filament rather than from said interposed part as in the case of discs 20 and 20a described above. Accordingly, the slot 22b in disc 2% can be of uniform width at its inward terminus and the tabs 34 formed by a suitable tool that is located outside of rather than within the filament.

Alternatively, the auxiliary locking means may comprise a plurality of radially spaced dimples or indents 36 such as those shown in dotted outline in Fig. 4. As illustrated, the aforesaid indents are disposed proximate and thus adapted to seat against the outer surface of the adjacent filament turnor turns and prevent the 'disc from slippin laterally from its inserted position.

It willbe recognized from the foregoing that the objects of the invention have been achieved by providing an improved filament support assembly and members which can be fabricated in a much simpler and more efficient manner than heretofore and wherein the support members are automatically and positively clamped in their position of use on the filament when inserted therein.

While several preferred embodiments have been illustrated and described, it will be understood that the invention is not limited thereto or thereby.

We claim:

1. In combination with a coiled filament of refractory wire comprising a plurality of spaced turns, a support member of refractory sheet material having an opening that extends inwardly from its periphery, said support member being inserted between adjacent turns of said filament and disposed transversely of said filament so that a part of one of said adjacent turns passes through said opening, said support member in the region interposed between said adjacent filament turns having a thickness greater than the spacing between said turns and, by virtue of the resultant spreading of said turns, being firmly gripped and compressively clamped thereby and prevented from being rotatively or laterally displaced from its inserted position on said filament.

2. In combination with a coiled filament of refractory wire comprising a plurality of uniformly spaced turns, a support member of refractory sheet material having an opening that extends inwardly from its periphery, said support member being inserted between adjacent turns of said filament and disposed transversely of said filament so that a part of one of said adjacent turns passes through said opening, said support member being greater in thickness than the spacing between said adjacent filament turns by an amount such that said support member, by virtue of the resultant spreading of said turns, is firmly gripped and compressively clamped thereby and prevented by such clamping from being rotatively or laterally displaced from its inserted position on said filament even when the latter is mounted under tension and is thus slightly distended.

3. In combination with a coiled filament of refractory metal wire comprising a plurality of spaced turns, a support member of refractory sheet material having an opening that extends inwardly from its periphery, said support member being inserted between adjacent turns of said filament and disposed transversely of said filament so that the inward terminus of said opening is located within the interior of said filament and a part of one of said adjacent turns passes through said opening, said support member in the region interposed between said adjacent turns having a thickness greater than the spacing between said turns and, by virtue of the resultant spreading of said turns, being firmly gripped and compressively clamped thereby in its inserted position and prevented from rotating about the axis of said filament, marginal portions of said support member at the inward terminus of said opening being bent into the interior of said filament and constituting projections that extend transversely from one side of said support member and are adapted to seat against the inner surface of the filament turn thcreat and to prevent the excessive lateral displacement of said support member should the latter accidentally be subjected to a displacing force greater than the compressive clamping force exerted by said filament.

4. In combination with a coiled linear filament of refractory metal Wire comprising a plurality of uniformly spaced turns, a metal support disc having a slot that extends radially inward from its periphery and merges with a centrally-located aperture, said disc being inserted between adjacent turns of said filament and positioned transversely thereof so that said aperture is substantially centered within the interior of said filament and a part of one of said adjacent filament turns passes through said slot, the thickness of said support disc being greater than the spacing between turns of said filament by an amount such that said disc, by virtue of the resultant spreading of said adjacent turns, is firmly gripped and compressively clamped thereby in its inserted position and prevented from rotating about the axis of said filament even when said filament is mounted under tension and is thus slightly distended, a plurality of tooth-like burrs at and protruding from the margin of said aperture and a side of said disc into the interior of said filament, said burrs being disposed to seat against the inner surface of the filament turn thereat and thereby prevent the excessive lateral displacement of said disc should the latter accidentally be subjected to a displacing force greater than the compressive clamping force exerted by said filament.

5. In combination with a coiled filament of refractory metal wire comprising a plurality of spaced turns, a support member of refractory sheet material having an opening that extends inwardly from its periphery, said support member being inserted between adjacent turns of said filament and disposed transversely of said filament so that a part of one of said adjacent turns passes through said opening, said support member in the region interposed between said adjacent turns having a thickness greater than the spacing between said turns and, by virtue of the resultant spreading of said turns, being firmly gripped and compressively clamped thereby in its inserted position and prevented from rotating about the axis of said filament, portions of said support member beyond the part thereof interposed between said adjacent turns being displaced from the body of said support member and constituting projections that extend transversely therefrom toward the outer surface of at least one of the adjacent filament turns and are adapted thereby to seat against said filament turn and prevent the excessive lateral displacement of said support member should the latter accidentally be sujected to a displacing force greater than the compressive clamping force exerted by said filament.

6. A support member adapted to be inserted into a coiled filament of refractory metal wire having a plurality of precisely spaced turns, said support member comprising a wafer-like body of refractory material having a thickness greater than the spacing etween the adjacent turns of said filament into which it is to be inserted, an opening in said body extending inwardly from the periphery thereof and adapted to receive a part of one of said adjacent turns of said filament, and a plurality of slits in said body that extend radially from the inward terminus of said opening and define a plurality of triangular-shaped tabular segments displaceable from the plane defined by said body into the interior of said filament when said support member is in its inserted position thereon.

7. The combination of a coiled refractory wire filament and a clamped transversely extending support member as set forth in claim 1 wherein portions of said supportmember adjacent said filament are displaced to form projections that extend transversely from the plane of said support member and are thereby adapted to seat against one of the adjacent turns of said filament and prevent excessive lateral displacement of said support member should the latter accidentally be subjected to a displacing force greater than the compressive clamping force exerted by said filament.

References Cited in the file of this patent UNITED STATES PATENTS 

